Add tests for LT-22576

[imnasnainaec]

Quick Summary

Tests requested by #1051 author, generated by Claude.

Devin review: https://app.devin.ai/review/sillsdev/FieldWorks/pull/1052

CI-ready checklist

• Commit messages follow .github/commit-guidelines.md (subject ≤ 72 chars, no trailing punctuation; if body present, blank line then ≤ 80-char lines).
• No whitespace warnings locally:

  git fetch origin
  git log --check --pretty=format:"---% h% s" origin/<base>..
  git diff --check --cached

• Builds/tests pass locally (or I've run the CI-style build via Bash script or MSBuild).
• If this is core-developer AI-assisted work, I followed Docs/workflows/ai-pr-workflow.md and ran pr-preflight or the equivalent branch-readiness review before requesting review.
• For any Src/** folders touched, corresponding AGENTS.md files are updated or explicitly confirmed still accurate.

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This change is 

[github-actions]

⚠️ Commit Message Format Issues ⚠️

commit 086024dd96:
3: B1 Line exceeds max length (86>80): "Cover IsFeatureBasedNCNameUserDefined and RuleFormulaSlice.OnDisplayContextSetFeatures"
5: B1 Line exceeds max length (85>80): "empty-selection contexts. The test control overrides GetCmObject, the extension point"
6: B1 Line exceeds max length (86>80): "concrete rule controls already implement, so the selection-to-context logic under test"